Copal varnish is one of the very finest varnishes for japanning purposes. It can be dissolved by linseed oil, rendered dry by adding some quicklime at a heat somewhat less than will boil or decompose the oil by it.
This solution, with the addition of a little turpentine, forms a very transparent varnish, which, when properly applied and slowly dried, is very hard and durable. This varnish is applied to snuff boxes, tea boards and other utensils. It also preserves paintings and renders their surfaces capable of reflecting light more uniformly.
If powdered copal be mixed in a mortar with camphor it softens and becomes a coherent mass, and if camphor be added to alcohol it becomes an excellent solvent of copal by adding the copal well ground, and employing a tolerable degree of heat, having the vessel well corked, which must have a long neck for the allowance of expansion, and the vessel must only be about one-fourth filled with the mixture. Copal can also be incorporated with turpentine, with one part powdered copal to twelve parts pure turpentine, subjected to the heat of a sand-bath for several days in a long-necked mattress, shaking it frequently.
Copal is a good varnish for metals, such as tin; the varnish must be dried in an oven, each coat, and it can be colored with some substances, but alcohol varnish will mix with any color.